Fig. 4: MEK1 regions were defined by enrichment screens and mapped to different protein domains.

a A schematic protocol of the tiling enrichment screens on MEK1. A375-Cas9 cell line were transduced with sgRNA library and treated with DMSO or one of the MEK inhibitors: selumetinib, trametinib, cobimetinib or binimetinib. The LFC values of each sgRNA between the drug treatment arm and DMSO arm at day 18 was determined. Different colours represent genomic integration and expression of different sgRNAs. The cell coverage and the timeline of the screens are indicated below the schematic protocol. b LFC values of each sgRNA in each screen were plotted to the MEK1 protein primary sequence. The most enriched sgRNAs are labelled as ‘sg + targeting residues’ and indicated by arrows for the binimetinib screen. Dots are coloured according to MEK1 domains. A-loop activation loop, K1-K4 core kinase domain 1–4, P-rich loop proline-rich loop. Data points represent mean of two replicates. c Overview of the MEK1 regions targeted by the most enriched sgRNAs, mapped to the protein crystal structure. MEK1 residues are colour-coded by sgRNA bins in a heatmap style. Colour codes of the sgRNA bins are indicated below the structures. Molecule in green: AMP-PNP, molecule in orange: binimetinib. d A close-up view of regions at Helix A, the β7-β8 loop and the C-terminus. e A close-up view of a region at MEK1 Helix C domain. f A close-up view of a region at the allosteric drug binding pocket. The highlighted residue M143 is the gatekeeper of the ATP binding pocket. c–f MEK1 protein ribbon is coloured in light green. MEK1 domains are labelled and indicated with arrows in grey. Key residues are displayed as ball-and-sticks, labelled and indicated by arrows in the same colours as the highly enriched region. PDB code for structures in (d, e) 7JUZ, in (c, f) 7M0U.